This invention relates to molding expandable rubbery compositions and articles molded therefrom. In one of its aspects, this invention relates to a process for molding sponge like articles. In still another of its aspects, this invention relates to the use of microwave energy in molding expandable thermoplastic elastomer compositions.
In the molding of compositions based on the combination of a thermoplastic block copolymer elastomer and a normally solid resinous polymer combined with the polarizing agent in sufficient amount to achieve rapid heating through response to microwave treatment, it is known that an article having a skin and a porous interior can be produced by the addition of blowing agent to the molding composition with subsequent melting and molding at temperatures sufficient to activate the blowing agent. It has now been discovered that by controlling the amount of blowing agent present in the molding compositions the porosity and skin thickness of the molded article can be controlled so that articles can be produced having relatively thin skin surrounding a sponge-like interior which are suitable for use in services where a soft feel and easy bending are desirable such as metatarsal supports.
In these products, structural integrity of the polymeric walls surrounding the interstitial voids is of great importance so that the shape of the molded article can be maintained. To maintain the load bearing strength of the cell walls, it has been found necessary when relatively large pores are produced in the blown, molded objects to introduce stabilizing compounds into the molding compositions to maintain the structural stability of the molded objects.
It is therefore an object of this invention to provide a molded polymeric material in which a central portion of sponge-like appearance is surrounded by a thin skin of highly dense material. It is another object of this invention to provide a method for preparing a molded article in which a thin skin of highly dense material surrounds a sponge-like interior. It is still another object of this invention to provide a molding composition and form from such composition a molded object having a thin skin surrounding a sponge-like interior.
Other aspects, objects and the various advantages of this invention will become apparent upon reading this specification and the appended claims.